Production of styrenes



United States Patent Claims. (Cl. 260669) This invention relates to a process for the production of styrenes by dehydrogenation of ethylbenzenes with oxygen in the presence of iodine.

It is known that saturated organic compounds can be converted into the corresponding olefinically unsaturated compounds by dehydrogenation with oxygen in the presence of free or combined halogen. The process is carried out in the gas phase at temperatures of from 450 C. to 800 C. According to the processof US. Patent No. 2,719,171, the reaction is carried out in a reactor which is either empty or which contains some inert material, such as glass or quartz, as a heat carrier. According to Example 4 of the said patent ethylbenzene is dehydrogenated at a conversion of 28.9% and with a yield of 39.3% of styrene. According to Example 30 of US. Patent No. 3,207,805, styrene is obtained in a yield of 94.9% at a conversion of 60.2% by reacting ethylbenzene with oxygen in the presence of ammonium iodide and a large amount of steam as diluent at 700 C. in contact with stationary ceramic material. In this process also the conversion is not satisfactory and moreover the recovery of the catalyst offers difliculties. In particular, relatively large reactors are necessary owing to the use of large amounts of steam as diluent.

It is an object of the present invention to provide a process for the production of styrenes by dehydrogenationof ethylbenzenes in which high yields can be obtained with high conversions. It is another object of this invention to provide a process for the productionof styrenes by dehydrogenation of ethylbenzenes in which the iodine used as catalyst may readily be recovered. In particular it is an object of this invention to provide a process for the production of styrenes by dehydrogenation of ethylbenzenes in which large amounts of steam are not necessary as diluent and which can be carried out in small reactors.

These and other objects of the invention are achieved in a process'for the production of styrenes by dehydrogenation of ethylbenzenes with oxygen in the presence of iodine and an inert heat carrier at temperatures of from 400' C. to 700 C., the inert heat carrier having an internal surface area of 0.1 to sq. m./g. and a mean pore size of 3300 to 30,000 A.

Surprisingly, yields of more than 95 are achieved in the new process at more than 90% conversion. In con- ,trast, in the methods which have hitherto been used industrially yields of more than 95% are only obtained provided the conversion does not exceed at a conversion of only the yield falls to below 90%. (Chem. Ing. Techn., volume 37 (1965) page 362, FIG. 2.) In the production of styrene the separation of the unreacted ethylbenzene by distillation from the reaction product is very expensive. The new process therefore brings with it a considerable saving in expense as a result of the high conversion. The reaction may also be carried out without any diluent at all so that small reactors may be used. Since there is no diluent to heat up, the heat balance of the reaction zone of the plant is positive. Excess reaction heat may be used to cover the requirements of the distillation necessary for the separation. The new process thus exhibits a favorable energy balance.

3,392,205 Patented July 9, 1968 Examples of ethylbenzenes which are suitable starting materials are ethylbenzene itse1f,.ethylbenzenes in which the ethyl group bears an alkyl radical having one or two carbon atoms as a substituent, such as.isopropyl benzene and butylbenzene, and also nuclear-chlorinated ethylbenzenes which preferably have one to four chlorine atoms attached to the benzene ring, such as 2-chloroethylbenzene, 4-chloroethylbenzene, 2,5-dichloroethylbenzene and 2,4,6trichloroethylbenzene.

Oxygen is usually employed in amounts of 0.35 to 1 mole per mole of ethylbenzene. Oxygen-containing gases, such as air, may also be used but it is preferred to use pure oxygen so that the reaction may be carried out in a very small reaction space.

Iodine is usually required only in very small amounts, for example 0.005 to 0.05 mole per mole of ethylbenzene, as catalyst. Inorganic or organic iodine compounds which are decomposed under the process conditions to form iodine or which are oxidized to iodine maybe used instead of iodine itself. Examples of suitable compounds are hydrogen iodide, ammonium iodide, ethyliodide and u,fl-diiodoethylbenzene.

The inert heat carriers used have an internal surface area of 0.1 to 15 sq. m./g., particularly 0.5 to 10 sq. m./g., and an average pore size of 300 'to 30,000 A., particularly 600 to 20,000 A. Those materials are regarded as inert which do not initiate any secondary reactions, particularly which do not initiate polymerization of the styrene, under the conditions of the process. In the investigation of many materials it has been found that substances which when suspended in Water have a pH value of more than 5.5, particularly of from 5.5 to 10, are particuarly Well suited. Materials which are more strongly acid than this are not regarded as inert. Examples of suitable inert materials are porcelain, alkaline earth metal silicates, aluminum oxide and Particularly pumice.

The reaction is carried out at temperatures of 400 to 700 C., particularly from 450 to 600 C. Atmospheric pressure is generally used but slightly subatmospheric pressure or slightly superatmospheric pressure may be used, for example 0.1 to 1 atmosphere gauge. The residence time may vary within wide limits, for example from 0.1 to 30 seconds, and it is preferably from 0.5 to 10 seconds.

The inert heat carrier may be stationarily arranged in the reaction chamber. Particulraly good results are achieved however in a fluidized bed, the particle size of the fluidized material usually being from 0.05 to 0.4 mm.

The process may advantageously be carried out by dissolving iodine or the iodine compound in the ethylbenzene, vaporizing the solution and passing the vapor together with oxygen into the reaction zone. When a fluidized bed is being used, the oxygen is advantageously injected immediately before and direct into the fluidized bed. The gas keeps the material in fluidized motion. The amount of oxygen is advantageously regulated so that the lowest possible amount of off-gas escapes. If a diluent is not used, practically the Whole reaction product is condensable. It is separated into an aqueous phase and an organic phase and the styrene is separated from the organic phase by distillation. Unreacted ethylbenzene may be reused. It is advantageous to treat the hot reaction product with thiosulfate solution or particularly with aqueous alkali to recover the iodine. The bulk of the iodine is then in the aqueous phase and, after acidification or acidification and oxidation, may be extracted with the ethylbenzene and returned to the process. Small amounts of iodine are also contained in the first ruunings and in the residue of the organic phase. First runnings and residue are advantageously burned. Iodine is either washed out from the combustion gases by means of Example 1 A total of 505 g. of ethylbenzene is passed through a. quartz fluidized-bed reactor having an internal diameter of 30 mm. of a filling of 100 ml. of Italian pumice having a particle size of 0.06 to 0.2 mm. (internal surface area 2.4 sq. m./g., mean pore radius 3150 A.) at 550 C. The hourly throughput is 1 mole of ethylbenzene, 0.02 mole of iodine and 0.7 mole of oxygen. The residence time under the reaction conditions is 3.1 seconds. 495 g. of organic reaction product is obtained. Analysis gives a content of unreacted ethylbenzene of 8.2% by Weight and of styrene of 87.8% by weight. From this a yield of 95.7% of the theory may be calculated at a conversion of 91.9%.

Example 2 Examples 3 to 7 The procedure of Example 1 is used but other heat carriers are used instead of pumice and the following results are obtained; ISA=internal surface area in sq. m./g.; MPR=mean pore radius in A.; SY=styrene yield in percent of the theory; -C=conversion in percent:

Example Heat carrier ISA MP R SY C 3 a-Aluminum oxide 8. 28 695 97 79.8 4.. Petroleum coke. 0.1 5,000 91 34. 6 5. 0. 1 28, 000 71 57 6- 0.1 1,600 74. 1 14. 1 7 38% of manganese dioxide and 178 42. 76. 5 41. 4

2% of lithium chloride on gamma-aluminum oxide (according to Example 1 of French patent specification No. 1,342,464).

Example 8 Dehydrogenation is carried out as described in Example 1 but with a stationary pumice catalyst instead of in a fluidized bed. A styrene yield of 87.5% of the theory is obtained with a conversion of 78.3%.

Example 9 0.7 mole of 1-ethyl-2,5-dichlorobenzene, 0.5 mole of oxygen and 0.018 mole of iodine per hour are reacted in contact with 200 ml. of Italian pumice in a fluidizedbed reactor according to Example 1. The residence time is 9.3 seconds. The total throughput is 810 g. The organic reaction product is 798 g. containing 44.9% by weight of unreacted starting product and 49.85% by weight of dichlorostyrene (yield: 88.9%, conversion 56.6%).

Example 10 The procedure of Example 9 is followed but using 270 g. of 1-ethyl-2,4,6-trichlorobenzene. The organic reaction product is 266 g. and contains 38.1% by weight of starting product and 41.6% by weight of trichlorostyrene. The yield is 73.7% and the conversion 59%.

Example 11 1 mole of isopropylbenzene, 0.8 mole of oxygen and 0.03 mole of iodine per hour are reacted at mm. Hg at 550 C. in the fluidized-bed reactor according to Example 1 in contact with 400 m1. of Italian pumice having a particle size of 0.1 to 0.4 mm. The residence time is 1.5 seconds. The total throughput is 432 g. The organic reaction product is 425 g. having a content of 46.6% by weight of isopropylbenzene and 49.6% by weight of u-methylstyrene. The yield is 90.7% and the conversion is 54.4%.

We claim:

1. In a process for the production of styrenes by dehydrogenation of ethylbenzenes with oxygen in the presence of iodine and an inert heat carrier at temperatures of from 400 C. to 700 C., the improvement which comprises using an inert heat carrier which has an internal surface area of 0.1 to 15 sq. m./g. and a mean pore size of 300 to 30,000 A.

2. A process as claimed in claim 1 carried out in a fluidized bed.

3. A process as claimed in claim 1 carried out in the absence of diluents.

4. A process as claimed in claim 1 wherein the inert heat carrier used has a pH value of more than 5.5 when suspended in water.

5. A process as claimed in claim 1 wherein aluminum oxide is used as the inert heat carrier.

6. A process as claimed in claim 1 wherein pumice is used as the inert heat carrier.

7. A process as claimed in claim 1 wherein the hot reaction product is treated with aqueous alkali solution to yield an aqueous and an organic phase, iodine is liberated from said aqueous phase and extracted with the said ethylbenzene, the first runnings and the residue from the distillation of said organic phase are burned and the iodine contained in the burned gas is washed out with said ethylbenzene.

8. A process as claimed in claim 7 wherein the iodine is liberated from the aqueous phase by acidification.

9. A process as claimed in claim 7 wherein the iodine is liberated from the aqueous phase by acidification and oxidation.

10. A process as claimed in claim 7 wherein the iodine is washed out from the burned gas with aqueous potassium iodide solution instead of with ethylbenzene.

References Cited UNITED STATES PATENTS 3,130,241 4/1964 Baijle et al. 260--680 3,304,329 2/1967 Jones et al. 260669 3,318,967 5/1967 Timms et al. 260680 DELBERT E. GANTZ, Primary Examiner, C. R. DAVIS, Examiner.

Patent No. 3,392,205

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION July 9, 1968 Rolf Platz et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 53, "3300" should read 300 Signed and sealed this 16th day of December 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, IR.

Edward M. Fletcher, Ir.

Commissioner of Patents Attesting Officer 

1. IN A PROCESS FOR THE PRODUCTION OF STYRENES BY DEHYDROGENATION OF ETHYLBENZENES WITH OXYGEN IN THE PRESENCE OF IODINE AND AN INERT HEAT CARRIER AT TEMPERATURES OF FROM 400*C. TO 700*C., THE IMPROVEMENT WHICH COMPRISES USING AN INERT HEAT CARRIER WHICH HAS AN INTERNAL SURFACE AREA OF 0.1 TO 15 SQ. M./G. AND A MEAN PORE SIZE OF 300 TO 30,000 A. 